Application.MainWindow Property

Gets or sets the main window of the application.

Namespace: System.Windows
Assembly: PresentationFramework (in presentationframework.dll)
XML Namespace:

public Window MainWindow { get; set; }
/** @property */
public Window get_MainWindow ()

/** @property */
public void set_MainWindow (Window value)

public function get MainWindow () : Window

public function set MainWindow (value : Window)

    <Window .../>

Property Value

A Window that is designated as the main application window.

Exception typeCondition


MainWindow is set from an application that's hosted in a browser, such as an XAML browser applications (XBAPs).

MainWindow is automatically set with a reference to the first Window object to be instantiated in the AppDomain.

You can specify a different main window by setting MainWindow assigning another Windows object to the MainWindow property.

If the ShutdownMode property of the Application object is set to OnMainWindowClose, closing the main window causes the application to shut down.

It is possible to set the MainWindow property from XAML, if an application's main window is not the window that is produced by setting the StartupUri property in XAML. The two limitations of the XAML approach are:

  • You can specify either a XAML-only Window or a XAML-only NavigationWindow as the main window.

  • You must set the Visibility property of the window you specify, otherwise it won't be shown.

The reference to the first Window object to be instantiated is also added as the first item to the Windows collection. If MainWindow is subsequently set with a reference to a different Window, the position of the item with the reference to the main window will change, while the order of items in Windows remains the same. Consequently, always use MainWindow to refer to the main window instead of the first item in Windows.


If the main window is a NavigationWindow, and you need specific access to NavigationWindow members, you will need to cast the value of MainWindow to NavigationWindow.

This property is available only from the thread that created the Application object.

The following example shows how to find the main application window.

// Get the main window
Window mainWindow = this.MainWindow;

The following example shows how to set MainWindow using XAML.

    <NavigationWindow Source="MainPage.xaml" Visibility="Visible"></NavigationWindow>

Windows 98, Windows Server 2000 SP4, Windows CE, Windows Millennium Edition, Windows Mobile for Pocket PC, Windows Mobile for Smartphone, Windows Server 2003, Windows XP Media Center Edition, Windows XP Professional x64 Edition, Windows XP SP2, Windows XP Starter Edition

The Microsoft .NET Framework 3.0 is supported on Windows Vista, Microsoft Windows XP SP2, and Windows Server 2003 SP1.

.NET Framework

Supported in: 3.0